Cool that your designing a putter. A favorite category of mine as a designer. I have always preferred a “face balanced” or “force balanced” design as a design that would work best for the most people. I understand that each individuals stroke should be analyzed and that each player will have preferences, but from a mass and dimensional characteristic standpoint face balanced designs make the most sense, in my opinion. Also, if you prescribe to the notion that there is a principle, basic set up that a player should have when putting – hands below the shoulders, arms hanging naturally, eyes over the ball – a face balanced putter will give the best chance for the clubface to stay square to the target line, with less rotation of the mass and less variation from the back stroke through the strike. We know that the face can not stay perfectly square throughout the entire stroke without manipulating something in the stroke, which is difficult to do consistently. By using a face balanced design, a simplified stroke with no hand manipulation, gives players the best chance to start the ball online, again, in my opinion. Important to understand that a “center shafted” design is not necessarily a “face balanced” design. It can be, if the bore and the shaft perfectly dissect the center of the mass, but I have seen many center shaft designs that don’t. Most face balanced designs are face balanced because they are designed to be used with a particular shaft with a specific bend for that putter head. So, you can do it with a center shaft, but the bore and the dissection of the mass must be really precise. With a heel side bore and using specific bends in putter shafts, you can simply manipulate the bends until you get to face balanced. Still has to be precise, but you can work with the shaft. A straight shaft in a center shafted design has no room for error IF the goal is to have it “face balanced”.
Hope this helps.